The long term goals of this research are to understand the mechanisms of latent infection by herpes simplex virus (HSV), specifically with regard to the role of the host immune response in regulating latent infection, the role of viral gene products in promoting latent infection, and the effect of viral latent infection on neuronal gene expression and function. In this application our specific aims are: 1. To further define how the host immune response affects latent infection by herpes simplex virus by. Defining how durable long-lasting immune responses are induced by replication-defective and replication-competent HSV strains by: a. Determining the duration of expression of vectored proteins and transcripts following immunization. b. Determining the duration of cytokine expression in tissue following injection of replication-defective mutant vectors. c. Determining the duration of populations of T cells specific for the vectored antigen. d. Defining how pre-existing anti-HSV immunity blocks viral DNA synthesis in ganglionic tissue; 2) To define mechanisms by which HSV gene products affect latency by: a. Defining the mechanisms by which the LATs down-regulate viral lytic gene expression by constructing and characterizing viral mutants with specific mutations in the LATs transcriptional unit. b. Defining the mechanisms by which ICP8 increases the acute levels of HSV DNA in ganglia by determining the mechanism by which ICP8 stimulates accumulation of viral DNA in neurons and defining the portions of ICP8 needed for stimulation of DNA accumulation; and 3) To define how HSV causes long-term effects on neuronal gene expression by: a. Performing in situ hybridization to define the cells in which the neuronal genes are expressed during latent infection. b. Performing northern blot hybridization to confirm the changes in gene expression. c. Studying mutant viral strains to determine the viral functions needed for long-term alteration of neuronal gene expression, as revealed by changes in neuronal gene expression measured on microarrays.